I couldn't track down these figures either. What I was able to find is that the Q factor of the "race" is 3mm less then the "trail". Just like what you said, except the Q factor of the 2X10 trail (38/26) is wider then the 2X10 "race". Not sure that this helps you, but figured I would throw it out there.

shimano has a gauging tool that goes into your bottom bracket to see if the narrow Q-factor cranks will fit your bike.. its an inexpensive cardboard tool shaped like the cranks... call them, they will probably send you one at no charge.

Technically speaking yes the q factor is a measure of the distance between the outside of the cranks, but, smaller q factor must also mean smaller inner width . . . you can't achieve smaller q by just shaving off the outer edge of the cranks, the crank arm is carefully designed for the maximum stiffness with minimal material, it needs to be a certain thickness, therefore narrowing the inner width to achieve it.